Summary Excess molar volumes of methyl tert-butyl ether (MTBE)+1-pentanol+octane and the binary mixtures MTBE+1-pentanol and 1-pentanol+octane, were measured at 298.15 K and atmospheric pressure, using a DMA 4500 Anton Paar densimeter. All the experimental values were compared with the results obtained by empirical expressions for estimating ternary properties from binary results.